DIPOL Weekly Review – TV and SAT TV, CCTV, WLAN

DAS (Distributed Acoustic Sensing) – Fibre optics as detectors.

Fibre optics enable the transmission of huge amounts of data over long distances. But is this their only advantage? No, as it turns out. Another important application for fibre optics is DAS (Distributed Acoustic Sensing) technology, which allows real-time measurements along the entire length of the cable. The principle behind distributed acoustic sensing DAS is quite simple. Every sound is a vibe which causes gentle movements of the optical fibres. These movements in turn cause interference to the transmitted light pulses. Analysing these interferences makes it possible to identify their nature and causes. Connected to one end of the cable, the DAS sensor sends optical pulses and analyses the light particles that return from each microscopic section of the cable. Any interference that is generated along the cable changes the properties of the light, thus providing information about the nature, location and intensity of the interference. This data is then processed and interpreted, thus creating a real-time acoustic profile of the environment.

Now, researchers are experimenting with DAS distributed acoustic detection technology in the immediate vicinity of railway lines. When a train moves along a section of track, vibrations are created which analysts can monitor in real time. If the signal suddenly changes, this could indicate, for example, a broken rail. The advantage of this approach over current monitoring systems is that it can work along the entire length of the track rather than at selected points along it. Currently, sensors monitoring the condition of the railway infrastructure, are distributed point-wise.

DAS technology has also found applications in the oil and gas industry, providing the ability to continuously monitor pipelines to detect leaks. As technology continues to evolve, the potential applications of DAS are growing exponentially. Advances in artificial intelligence, machine learning and data analytics are enhancing the capabilities of this technology, enabling more sophisticated and accurate interpretations of the data collected.

How to power an IP device without PoE using twisted-pair cable?

When an IP device, e.g. a camera, that does not support PoE 802.3af/at standard needs to be installed in a place where only twisted-pair cable is laid, there is a problem with its power supply. The solution can be to use a PoE adapter N9205 which allows to transmit data and power through one UTP cable (data on wires 1, 2, 3, and 6, and power on wires 4, 5, 7, and 8).

Measurements in fiber optic systems. Part 2.4 – transmission measurement – why measure at 1310 nm and 1550 nm?

Verifying the correctness of a fibre optic system built using single mode fibre optics should include measurement at 1310 nm and 1550 nm. Even if only 1310 nm SFP inserts are to function in this network, you should be sure that in the event of changing them for e.g. 1310 nm/1550 nm WDM inserts, the network will function correctly.

Measurements for the two wavelengths may give slightly different results and highlight some problems in the system that would not be identified with only one measurement. The first factor affecting the difference in the result is the different unit attenuation of the fibre for the different wavelengths (find out more here). However, this is irrelevant for short distances – only for distances of more than 1000 m can the difference exceed 0.1 dB and it should increase linearly by about another 0.1 dB for a further 1000 m. For shorter links, the measurement results should be similar with slightly less attenuation for the 1550 nm wavelength.

If the measurement for the 1550 nm wavelength gives a worse result, this most likely indicates a macro-bend in the fibre somewhere along the route. Often this is a bend in the switch – one that is easily found with the VFL visual fault locator. A clear light leakage will be seen at the bend location. However, it may be that the fibre bend is a consequence of a cable bend somewhere along the route. If this is the case, the transmission method will not give an answer about the exact location of the damage. Verification with an OTDR is necessary.

In the opposite case, when the measurement for 1310 nm gives a worse result (and the difference is greater than that due to the attenuation of the fibre), then this most likely indicates a problem with the positioning of the fibre, or to be more precise, the fibre cores. As a rule, this will be a problem somewhere at the connector(s), but it could also be a matter of a poorly made splice. Of course, without additional diagnostics using an OTDR, the possible location of the fault can only be done by trial and error.

It is worth considering why a wavelength of 1550 nm will highlight fibre bends and 1310 nm will highlight inferior fibre splices. To determine this, it is necessary to look at the structure of an optical fibre and introduce the definition of the fibre's MFD (Mode Field Diameter).

The structure of a typical optical fibre comprises a core and a surrounding sheath. These have different indexes of refraction (the core slightly larger), so that light introduced into the core at the right angle is completely internally reflected and propagates from the transmitter to the receiver. The physical diameter of the core is, of course, constant and can be, for example, 8.2 µm, regardless of the wavelength it carries. However, light waves do not propagate only in the core. Some of them are also transmitted in the sheath, and the area of the core and sheath that is responsible for the propagation of the light waves is the aforementioned MFD also referred to as the effective core area. It is the diameter of the MFD that is quoted by fibre manufacturers as the basic parameter of the fibre. The physical diameter of the core is of secondary importance. An example MFD value for a Corning SMF-28e+ fibre complying with ITU-T recommendation G.652.D, is 9.2 µm at 1310 nm and 10.4 µm at 1550 nm.

The fact that the MFD is different for different wavelengths may affect the measurements as described above. The larger diameter for 1550 nm means that the signal for this wavelength runs closer to the sheath border. Exceeding the minimum bending radius of the fibre will therefore result in greater attenuation for this wavelength, as some of the signal will 'escape' from the sheath more quickly. Conversely, the smaller MFD area for 1310 nm means that it will be more sensitive to the offset of the cores in relation to each other.

This was the last note in a series of notes on measurements in fibre optic systems with a focus on the transmission method. The topics of all previous notes are summarised below. We will continue with the topic of measurements in the near future, but we will focus on the detailed information related to Tier 2 measurements, i.e. OTDR reflectometry measurements.

DVB-T2 and DVB-S/S2 from two satellite positions in one fibre optic cable.

Fiber optic systems are playing an increasingly important role in the transmission of RF/SAT signals. They guarantee low signal loss and very high immunity to interference. Dipol offers a solution from TERRA, which allows to implement SMATV systems using optical fibers. The TERRA system for distribution of RF/SAT signals is distinguished by high quality and competitive price.

Key features of the system:

Below is an example of TERRA's optical-copper RF/SAT system solution.

Is it possible to control the third and fourth door in Hikvision IP video door entry system with one door station?

Depending on the model, Hikvision IP/2-Wire video intercom door stations have up to two relay outputs dedicated to control the wicket and entrance gate. Although an additional DS-K2M061 G77253 controller module can be connected to the door stations via the RS-485 bus, this module enables the user to replace the second relay output in the door station in order to increase security of the opening, and not to add an additional output. A solution to this problem can be use of relay outputs in the video door entry monitor e.g. DS-KH6320-WTE1 G74001 provided that the monitor has been provided with additional cabling for such integration. The monitor has two relay outputs that can be set as mono or bistable. Activation of the outputs from the monitor's GUI and configuration is done in the Settings ->Advanced Settings -> Output Settings tab. The outputs can be set for a specific time (1-180 s) or until they are deactivated by the user. After enabling the outputs, an icon will appear in the main window of the monitor, allowing you to enter the control options. The outputs will also be visible from within the Hik-Connect application.

Hotel TV. A headend is a basic device or a group of devices dedicated to facilities and institutions where it is desirable to centrally manage the program offerings distributed in the TV system. In addition to the headend consisting of modules according to the installer choice (transmodulators, amplifiers, optical transmitters, IP streamers) for receiving and converting the TV signals, the system comprises also the antenna assembly (satellite antennas, terrestrial TV and FM antennas)...>>>more